According to technical development and an increase in demands regarding mobile devices, demands for secondary batteries as an energy source are rapidly increasing. Generally, nickel cadmium batteries or hydrogen ion batteries have been used as secondary batteries, but recently, lithium secondary batteries that have very low self-discharge rates, have high energy densities, and are freely charged and discharged because a memory effect is barely generated compared to nickel-based secondary batteries, are widely used.
Such a lithium secondary battery mainly uses a lithium-based oxide and a carbon material respectively as a positive electrode active material and a negative electrode active material. The lithium secondary battery includes an electrode assembly, in which a positive electrode plate and a negative electrode plate on which the positive electrode active material and the negative electrode active material are respectively coated are arranged with a separator therebetween, and an exterior material, i.e., a battery case, that seals and accommodates the electrode assembly with an electrolyte.
The lithium secondary battery includes a positive electrode, a negative electrode, a separator disposed therebetween, and an electrolyte, and is classified into a lithium ion battery (LIB), a polymer lithium ion battery (PLIB), or the like based on which positive electrode active material and negative electrode active material are used. Generally, an electrode of the lithium secondary battery is formed by coating the positive or negative electrode active material on a current collector, such as an aluminum or copper sheet, a mesh, a film, a foil, or the like, and then drying the positive or negative electrode active material.
Generally, in a battery module of the secondary battery, cartridges accommodating battery cells are provided in a plural number and are stacked on each other, and such a plurality of cartridges are surrounded by a cover and then the cover is locked by a locking member, such as a bolt. Here, when the locking member, such as a bolt, directly contacts and pressurizes the cartridge that is, for example, a plastic injection molded body, the injection molded body may be damaged, and thus in order to prevent this, a bushing member is inserted first, and then the locking member, such as a bolt, is inserted into the bushing member.
However, the cartridge may be prevented from being damaged because a body portion of the bolt contacts the bushing member, but since a head portion of the bolt directly contacts the cover, when the bolt is rotated for locking, the head portion of the bolt pressurizes the cartridge adhered to the cover, and thus the cartridge may be damaged.